Field
Examples of the present disclosure generally relate to forming nanostructures in a film layer. Particularly, embodiments of the present disclosure provide methods for forming nanostructures with precision dimension control and minimum lithographic related errors
Description of the Related Art
In the manufacture of integrated circuits (IC), or chips, patterns representing different layers of the chip are created by a chip designer. A series of reusable masks, or photomasks, are created from these patterns in order to transfer the design of each chip layer onto a semiconductor substrate during the manufacturing process. Mask pattern generation systems use precision lasers or electron beams to image the design of each layer of the chip onto a respective mask. The masks are then used much like photographic negatives to transfer the circuit patterns for each layer onto a semiconductor substrate. These layers are built up using a sequence of processes and translate into the tiny transistors and electrical circuits that comprise each completed chip. Thus, any defects in the mask may be transferred to the chip, potentially adversely affecting performance. Defects that are severe enough may render the mask completely useless. Typically, a set of 15 to 100 masks is used to construct a chip and can be used repeatedly.
With the shrink of critical dimensions (CD), present optical lithography is approaching a technological limit at the 45 nanometer (nm) technology node. Next generation lithography (NGL) is expected to replace the conventional optical lithography method, for example, in the 32 nm technology node and beyond. The images of the patterned mask are projected through the high-precision optical system onto the substrate surface, which is coated with a layer of photoresist layer. The patterns are then formed on the substrate surface after complex chemical reactions and follow-on manufacturing steps, such as development, post-exposure bake and wet or dry etching.
Multiple patterning technique is a technology developed for photolithography to enhance the feature density. A simple example for utilizing the multiple patterning technique is double patterning, where a conventional lithography process is enhanced to produce double the expected number of features. Double exposure is a sequence of two separate exposures of the same photoresist layer using two different photomasks. This technique is commonly used for patterns in the same layer which look very different or have incompatible densities or pitches.
Double patterning lithography (DPL) is an effective technique to improve resolution. DPL theoretically doubles resolution through pitch splitting. DPL involves two separate exposures and etch steps (litho-etch-litho-etch, or called LELE or L2E2). DPL is particularly suitable for 20 nm generation technology and is one of the promising candidate solutions for scaling down to 14 nm technology and beyond. In some structures that require feature pitch down under 10 nm, higher number of the patterning technique, such as quadruple patterning or octuple patterning (L4E4 or L8E8), may be required to push the dimension limit. However, the lithography exposure process is an expensive process. Multiple practices of the lithography exposure processes for just a single layer patterning not only time consuming, but also significantly increase manufacturing cost. Furthermore, as well known in the art, overlay errors (or pattern registration errors) between layers are often inevitable during the lithographic exposure process. Thus, multiple exposure process on a single layer may enhance undesired overlay errors that may be detriment to device performance. With the shrink of critical dimensions (CD), overlay error in the critical layers of the device structure must be minimal or eliminated in order to reliably produce devices with minimal feature sizes.
Therefore, there is a need for forming nanostructures with precision dimension control and minimum lithographic related errors.